Conventionally, display devices (hereinafter, “3D display devices”) have been developed, which display a three-dimensional image (hereinafter, “3D image”) that represents depth, by using a stereo image that includes two images having a parallax difference between two viewpoints, and an image to which a depth map that illustrates the depth for each pixel of the image is attached. The range of depth (hereinafter, “depth range”) that can be reproduced on the 3D display device varies from device to device. Furthermore, the depth range of an image input to the 3D display device (hereinafter, “input image”) is different from the reproducible depth range of the 3D display device to which the image is output; and therefore the depth range of the input image needs to be converted (corrected) to a depth range suitable for the outputting 3D display device for displaying the 3D image. If the image is displayed on the 3D display device without performing conversion of the depth range, the front or back side of the image may become blurred, or the image may appear with insufficient depth. Methods of converting the depth range include a method of sequentially correcting the depth range so that a desired parallax amount can be achieved.
With some of the depth range converting methods of the conventional technologies, however, the depth after the conversion is excessively reduced so that the image output and displayed onto the 3D display device may look flat.